Tetrahydrofuran (hereinafter sometimes abbreviated as “THF”) is a useful compound as a solvent for various organic compounds including polymer compounds, a raw material for polytetramethylene glycol, and the like.
Tetrahydrofuran is frequently produced industrially by a dehydration cyclization reaction of 1,4-butanediol (hereinafter sometimes abbreviated as “1,4BG”). It is known that an acid catalyst is effective as a catalyst for this reaction in any of a homogeneous system or a heterogeneous system.
For example, there is known a method of using a solid catalyst such as a silica alumina catalyst (Patent Document 1), a cation exchange resin (Patent Document 2), etc. This method encounters such a problem that the catalyst deterioration under a high-temperature condition is serious, or the like. In recent years, there is also proposed a method for producing tetrahydrofuran by using a heteropolyacid which is considered to be small in the catalyst deterioration even under a high-temperature condition (Patent Document 3).
When THF is produced by a dehydration cyclization reaction of 1,4BG by using such a catalyst, a liquid phase reactor using a fixed bed reactor, a reactive distillation mode in which a product is distilled off from a reactor through a gas phase part, and the like are used.
Though such a process is operated in a state where a high-boiling component formed as a by-product during the reaction is accumulated in a liquid phase part of the reactor, the formation of a by-product solid is advanced at the same time.
Specifically, Patent Document 3 describes that deposition of a by-product solid such as a polymer, etc. makes the operation difficult and describes the formation of a solid derived from 2-(4-hydroxybutoxy)-tetrahydrofuran (hereinafter sometimes abbreviated as “BGTF”) that is a reaction by-product at the time of synthesis of 1,4BG and which is contained as an impurity in a raw material 1,4BG. In order to avoid such deposition of a by-product solid at the time of production of THF, Patent Document 3 describes that a pretreatment method of the catalyst is specified, the content of nitrogen is kept low, or the like.